This invention relates to a fuel heating system and particularly, to a system for heating fuel oil within a fuel tank before it is conducted into a fuel delivery circuit.
Diesel engine powered machines such as motor vehicles, stationary generating plants, and other fuel oil combustion devices are often operated in environmental conditions wherein the fuel oil and fuel delivery circuit are subjected to cold ambient temperatures. At sufficiently low temperatures, fuel oils become viscous, and develop paraffin or wax particles. These fuels have characteristic temperatures at which they become "cloudy" due to the pressure of dispensed wax crystals and at which they "freeze" or become a semi-solid mass, referred to as their cloud and pour points, respectively. Often fuel oil in use is exposed to these critical temperatures. Some diesel engine fuels have a cloud point of 20 degrees Fahrenheit and a pour point of 0 degrees Fahrenheit. Additionally, water which invariably is mixed with the fuel oil can freeze, forming ice particles. Such conditions may severely restrict fuel flow within the fuel delivery circuit, leading to reduced power output or complete inoperability of the associated fuel consuming device. Such problems obviously occur when the fuel reduces the point of solidification. Cloudy fuel may also lead to fuel flow restrictions when the suspended wax particles accumulate in filter elements and at other points in the fuel system. One method of preventing this condition is to maintain the fuel temperature above its cloud and pour points. This approach, however, is not always possible since adequate heat or power may not be available during storage periods, or while the associated fuel oil fired device is not operating.
In order to address such problems, many users of fuel oil combustion devices such as diesel engines provide fuel processing devices within the fuel delivery circuit. A number of such devices are described by my previously issued U.S. Pat. Nos.: 4,368,716; 4,428,351; 4,395,996; 4,421,090; and my currently pending patent applications; Ser. Nos.: 463,041, filed Feb. 1, 1983; 573,292, filed Jan. 23, 1984; and 653,854, filed Sept. 24, 1984. Many of the fuel processors and fuel heating apparatuses described by the preceding patents and patent applications further provide water separation and particulate filtration functions. Although these devices are entirely satisfactory in heating fuel drawn from a fuel reservoir in sufficiently cold ambient temperatures or when prolonged cold soaking occurs, it may be difficult or impossible to draw fuel from the fuel tank. In such conditions, the fuel oil within the fuel tank can become an essentially immovable mass of completely waxed fuel. In addressing such problems, designers of fuel heating systems in the past have attempted to overcome such difficulties by supplying a sufficient level of heat energy to the fuel tank to melt the entire contents. However, such approaches require such extremely high power requirements as to be inefficient or prohibitive.
In view of the above, it is an object of this invention to provide an apparatus which acts to warm fuel within a fuel tank prior to its introduction into the remainder of the fuel delivery circuit. It is a further object of this invention to accomplish such fuel heating using a minimal power input requirement. Additional objects of the invention are to provide such fuel heating employing a minimum of components and providing a system simple in configuration and operation.
The above objects of this invention are achieved by employing a fuel processor device which acts as a small-capacity fuel reservoir which provides warmed fuel for initial operation, and a larger capacity main fuel reservoir which holds the bulk of the stored fuel. The larger capacity main fuel reservoir includes heating means associated with the fuel processor to provide a sufficient flow rate of warmed fuel to sustain continued operation of the associated fuel oil fired device. High overall thermal efficiency is provided by heating a very small quantity of fuel oil for initial start-up and by providing a steady state energy input level into the main fuel reservoir which warms fuel to provide a flow rate of warmed fuel related to the fuel consumption rate of the fuel consuming device. No attempt need be made in accordance with this invention to maintain the entire contents of the main fuel reservoir in a wax-free state, even while the fuel consuming device is operating.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.